gistfile1.rb

# provider 
action :set do
  chef_config = ""
  if node[:ec2][:userdata]
    chef_config = JSON.parse(node[:ec2][:userdata])
    if chef_config.kind_of?(Hash)
      chef_config  = chef_config["attributes"]["run_list"]
      if chef_config.kind_of?(Array)
        chef_config = chef_config.first.split(/\[|\]/).last.gsub("_","-")
      end
    end
  elsif node[:roles]
    if node[:roles].kind_of?(Array)
      chef_config = node[:roles].first
    else
      chef_config = node[:roles]
    end
  end
  hostname = chef_config + "-" + node[:ec2][:instance_id].split("-").last
  execute "set_hostname" do
    command "hostname #{hostname}"
  end
  template "/etc/hosts" do
    variables(:hostname_fqdn => "#{hostname}.mydomain.com", :hostname => hostname)
    source "etc_hosts.erb"
    mode "0664"
  end
  ohai "Ohai reload" do
    action :reload
  end
end

# recipe:
  e = system_config_hostname "set my hostname" do
    action :nothing
  end
  e.run_action(:set)